The present invention relates to antistatic, thermoplastic polyurethane comprising ethylmethylimidazole ethyl sulfate, to a process for production of antistatic, thermoplastic polyurethane comprising ethylmethylimidazole ethyl sulfate, and to the use of ethylmethylimidazole ethyl sulfate for the production of antistatic, thermoplastic polyurethane.
Further embodiments of the present invention are found in the claims, in the description, and in the examples. It is, of course, possible to use the abovementioned features, and the features that will be explained below, of the inventive subject matter not only in the respective combination given but also in other combinations, without exceeding the scope of the invention.
Static charges can arise on electrical nonconductors or on articles or persons insulated via nonconductors, and are often undesired and detrimental, and sometimes dangerous.
The electrical nonconductors are often polymers. Since these polymers mostly cannot be replaced by conducting materials, attempts are made to increase the conductivity of the polymers via addition of antistatic additives, and thus to ground the articles or materials concerned. Polymers which comprise antistatic additives and whose volume resistivity measured to IEC 60093 is smaller than 1010 Ω/cm are hereinafter termed antistatic polymers. If the volume resistivity of antistatic materials is smaller than 108 Ω/cm, an article manufactured from said material is an “Electronic Sensitive Device” (EDS).
These antistatic polymers are versatile. Antistatic polymers are used not only for shoe-sector applications but also for elastomer rollers, in the sector of manufacturing of electronically sensitive components, and particularly in the sector of pneumatic conveying of solids.
Antistatic additives and antistatic polymers are known. By way of example, DE 3531660 describes antistatic polyurethane shoe soles. The antistatic effect is achieved via from 0.01 to 0.3% by weight of chemically bonded sulfonate groups. The volume resistivities achieved are <108 Ω/cm.
The use of various quaternary ammonium salts for increasing the conductivity of polymers is described in EP 1134268. This involves modifications of commercially available antistatic agents, such as Catafor F® or Catafor PU® from Rhodia. For example, volume resistivities of about 107 Ω/cm are achieved at high concentrations.
The examples of EP 1134268 show marked dependency of volume resistivity on humidity.
DE 3528597 describes the use of carbon blacks as conductivity improvers. Volume resistivities<109 Ω/cm are achieved. A disadvantage here is the black coloring of the product and a reduced level of mechanical properties when relatively large amounts of carbon black are used.
WO 2004/005391 relates to the use of ionic liquids in polymers as plasticizers, but also discloses that the ionic liquids simultaneously have an antistatic-additive effect. Polymers that can be used include, inter alia, elastomeric or crosslinked polyurethanes.
A disadvantage of the prior art is that the volume resistivity of this type of polymer is sometimes still very high, >108 Ω/cm, and that volume resistivities are dependent on humidity. The result can be static charges despite the presence of conductive additives.
A further disadvantage of the antistatic additives proposed in the prior art is that some of them have inadequate long-term effectiveness, the result being that in particular instances the volume resistivity of the polymers increases after as little as a few days.
Finally, high levels of addition of known antistatic additives impair the properties of the materials.
A further problem of known antistatic additives is that these cannot be used in particular in the thermoplastic processing and further processing of thermoplastic polyurethane, since few of these additives withstand the exposure to temperatures of about 220° C., sometimes repeated, in each case for from 5 to 10 minutes, which is necessary for thermoplastic processing and further processing. Furthermore, interactions of the antistatic additives with the polymer matrix often occur under the conditions of thermoplastic processing of polyurethane, the result being an adverse effect on the polymer matrix, for example via degradation of the polymer chains.
The additive must moreover have adequate compatibility with the polymer matrix during processing with thermoplastic polyurethane, so that it does not separate during melting, and so that it is not lost from the final product via exudation or evaporation. A further intention is that the mechanical properties of the thermoplastic polyurethane, for example abrasion or elastomeric properties, are not markedly impaired via addition of the additive.
It was therefore an object of the present invention to provide an antistatic thermoplastic polyurethane which does not exhibit the disadvantages stated above. In particular, it was an object of the present invention to provide an antistatic polyurethane which can be subjected without difficulty to thermoplastic processing, and which does not have any adverse effect on the matrix of the polyurethane, and which gives no excessive exudation of the antistatic additive after production of the antistatic thermoplastic polyurethane.